Method of removing sulfur dioxide from flue gases and treatment of oxidized effluent therefrom

Abstract

A method of removing sulfur dioxide from flue gases using calcium and magnesium scrubbing components and treatment of oxidized effluent from such a system includes passing classified oxidized effluent to a regeneration tank and adding lime to produce a regenerator discharge containing magnesium hydroxide, gypsum and crystalline inert material. Gypsum is separated from the discharge and a magnesium hydroxide stream passed to a concentration system to produce a concentrated solids stream of magnesium hydroxide, residual minor amount of gypsum and crystalline inert material. A portion of the resultant stream is returned to the sulfur dioxide removal system while a portion is passed to the oxidizer. Further portions may be fed to a power plant boiler or to the flue gas stream between a solids collection device and the wet scrubber.

1. In a method of removing sulfur dioxide from a flue gas stream of a power plant boiler by contact in a wet scrubber with an aqueous scrubbing slurry containing magnesium and calcium scrubbing components, and inert material in crystalline form, wherein calcium and magnesium sulfites and sulfates are formed, and the calcium sulfites and magnesium sulfites, following said contact, are oxidized in an oxidizer to produce an oxidized effluent containing magnesium sulfate and gypsum, along with said crystalline inert material which has been converted to an amorphous inert material, and the oxidized effluent passed to a separator to remove a major portion of the gypsum and produce a clarified oxidized effluent, the improvement comprising:
 passing the clarified oxidized effluent to a regeneration tank and adding lime slurry thereto to produce a regenerator discharge containing magnesium hydroxide, gypsum and regenerated crystalline inert material; 
 passing the regenerator discharge to a separator where a substantial amount of gypsum is separated therefrom and a separated magnesium hydroxide stream is provided containing magnesium hydroxide, a residual minor amount of gypsum, and regenerated crystalline inert material; 
 passing the separated stream to a concentration system to produce a concentrated solids steam containing a mixture of magnesium hydroxide, residual minor amount of gypsum and regenerated crystalline inert material; and 
 returning a portion of the concentrated solids stream to the magnesium-enhanced calcium slurry sulfur dioxide removal process while passing a remaining portion thereof to the oxidizer. 
 
     
     
       2. The method as defined in  claim 1  wherein a further remaining portion of the concentrated solids stream is fed to the power plant boiler for reaction with sulfur trioxide therein. 
     
     
       3. The method as defined in  claim 1  where a further remaining portion of the concentrated solids stream is fed to the power plant boiler for slag control. 
     
     
       4. The method as defined in  claim 1  wherein a further remaining portion of the concentrated solids stream is fed to the flue gas stream at a solids collection device selected from an electrostatic precipitator and a baghouse to react with sulfur trioxide present in the flue gas stream upstream of the wet scrubber. 
     
     
       5. The method as defined in  claim 1  wherein the calcium scrubbing component in the aqueous scrubbing slurry is lime. 
     
     
       6. The method as defined in  claim 1  wherein the calcium scrubbing component in the aqueous scrubbing slurry is limestone. 
     
     
       7. The method as defined in  claim 1  wherein the concentration system comprises stacked membrane filters. 
     
     
       8. In a method of removing sulfur dioxide from a flue gas stream of a power plant boiler by contact in a wet scrubber with an aqueous scrubbing slurry containing magnesium and lime, and inert material in crystalline form, wherein calcium and magnesium sulfites and sulfates are formed, and the calcium sulfites and magnesium sulfites, following said contact, are oxidized in an oxidizer to produce an oxidized effluent containing magnesium sulfate and gypsum, along with said crystalline inert material which has been converted to an amorphous inert material, and the oxidized effluent passed to a separator to remove a major portion of the gypsum and produce a clarified oxidized effluent, the improvement comprising:
 passing the clarified oxidized effluent to a regeneration tank and adding lime slurry thereto to produce a regenerator discharge containing magnesium hydroxide, gypsum and regenerated crystalline inert material; 
 passing the regenerator discharge to a separator where a substantial amount of gypsum is separated therefrom and a separated magnesium hydroxide stream is provided containing magnesium hydroxide, a residual minor amount of gypsum, and regenerated crystalline inert material; 
 passing the separated stream to a concentration system, including stacked membrane filters, to produce a concentrated solids steam containing a mixture of magnesium hydroxide, residual minor amount of gypsum and regenerated crystalline inert material; 
 returning a portion of the concentrated solids stream to the magnesium-enhanced calcium slurry sulfur dioxide removal process while passing a remaining portion thereof to the oxidizer; and returning a further remaining portion of the concentrated solids stream to the power plant boiler. 
 
     
     
       9. In a method of removing sulfur dioxide from a flue gas stream of a power plant boiler by contact in a wet scrubber with an aqueous scrubbing slurry containing magnesium and lime, and inert material in crystalline form, wherein calcium and magnesium sulfites and sulfates are formed, and the calcium sulfites and magnesium sulfites, following said contact, are oxidized in an oxidizer to produce an oxidized effluent containing magnesium sulfate and gypsum, along with said crystalline inert material which has been converted to an amorphous inert material, and the oxidized effluent passed to a separator to remove a major portion of the gypsum and produce a clarified oxidized effluent, the improvement comprising:
 passing the clarified oxidized effluent to a regeneration tank and adding lime slurry thereto to produce a regenerator discharge containing magnesium hydroxide, gypsum and regenerated crystalline inert material; 
 passing the regenerator discharge to a separator where a substantial amount of gypsum is separated therefrom and a separated magnesium hydroxide stream is provided containing magnesium hydroxide, a residual minor amount of gypsum, and regenerated crystalline inert material; 
 passing the separated stream to a concentration system to produce a concentrated solids steam containing a mixture of magnesium hydroxide, residual minor amount of gypsum and regenerated crystalline inert material; 
 returning a portion of the concentrated solids stream to the magnesium-enhanced calcium slurry sulfur dioxide removal process while passing a remaining portion thereof to the oxidizer; and returning a further remaining portion of the concentrated solids stream to the flue gas stream at a solids collection device, selected from an electrostatic precipitator and a baghouse, to react with sulfur trioxide present in the flue gas stream upstream of the wet scrubber. 
 
     
     
       10. A method of treating a bleed steam from a magnesium-containing portion of an oxidized effluent, of a magnesium-enhanced calcium slurry sulfur dioxide removal process, containing crystalline inert material, from an oxidizer, the oxidized effluent, after clarification, containing magnesium sulfate, and up to about three weight percent of amorphous inert material and gypsum fines, comprising:
 passing the oxidized effluent to a regeneration tank and adding lime slurry thereto to produce a regenerator discharge containing magnesium hydroxide, gypsum and regenerated crystalline inert material; 
 passing the regenerator discharge to a separator where a substantial amount of gypsum is separated therefrom and a separated magnesium hydroxide stream is provided containing magnesium hydroxide, a residual minor amount of gypsum, and regenerated crystalline inert material; 
 passing the separated stream to a concentration system to produce a concentrated solids steam containing a mixture of magnesium hydroxide, residual minor amount of gypsum and regenerated crystalline inert material; and 
 returning a portion of the concentrated solids stream to the magnesium-enhanced calcium slurry sulfur dioxide removal process while passing a remaining portion thereof to the oxidizer. 
 
     
     
       11. The method as defined in  claim 10  wherein a further remaining portion of the concentrated solids stream is fed to a power plant boiler for reaction with sulfur trioxide therein. 
     
     
       12. The method as defined in  claim 10  where a further remaining portion of the concentrated solids stream is fed to a power plant boiler for slag control. 
     
     
       13. The method as defined in  claim 10  wherein a further remaining portion of the concentrated slurry stream is fed to a flue gas stream at a solids collection device selected from an electrostatic precipitator and a baghouse to react with sulfur trioxide present in the flue gas stream upstream of the wet scrubber. 
     
     
       14. The method as defined in  claim 10  wherein a calcium scrubbing component of the magnesium-enhanced calcium slurry in the sulfur dioxide removal process is lime. 
     
     
       15. The method as defined in  claim 10  wherein a calcium scrubbing component of the magnesium enhanced calcium slurry in the sulfur dioxide removal process is limestone. 
     
     
       16. The method as defined in  claim 10  wherein the concentration system comprises stacked membrane filters. 
     
     
       17. A method of treating a bleed steam from a magnesium-containing portion of an oxidized effluent, of a magnesium-enhanced lime slurry sulfur dioxide removal process, containing crystalline inert material, from an oxidizer, the oxidized effluent, after clarification, containing magnesium sulfate, and up to about three weight percent of amorphous inert material and gypsum fines, comprising:
 passing the oxidized effluent to a regeneration tank and adding lime slurry thereto to produce a regenerator discharge containing magnesium hydroxide, gypsum and regenerated crystalline inert material; 
 passing the regenerator discharge to a separator where a substantial amount of gypsum is separated therefrom and a separated magnesium hydroxide stream is provided containing magnesium hydroxide, a residual minor amount of gypsum, and regenerated crystalline inert material; 
 passing the separated stream to a concentration system to produce a concentrated solids steam containing a mixture of magnesium hydroxide, residual minor amount of gypsum and regenerated crystalline inert material; 
 returning a portion of the concentrated solids stream to the magnesium-enhanced calcium slurry sulfur dioxide removal process while passing a remaining portion thereof to the oxidizer; and returning a further remaining portion of the concentrated solids stream to a power plant boiler. 
 
     
     
       18. A method of treating a bleed steam from a magnesium-containing portion of an oxidized effluent, of a magnesium-enhanced lime slurry sulfur dioxide removal process, containing crystalline inert material, from an oxidizer, the oxidized effluent, after clarification, containing magnesium sulfate, and up to about three weight percent of amorphous inert material and gypsum fines, comprising:
 passing the oxidized effluent to a regeneration tank and adding lime slurry thereto to produce a regenerator discharge containing magnesium hydroxide, gypsum and regenerated crystalline inert material; 
 passing the regenerator discharge to a separator where a substantial amount of gypsum is separated therefrom and a separated magnesium hydroxide stream is provided containing magnesium hydroxide, a residual minor amount of gypsum, and regenerated crystalline inert material; 
 passing the separated stream to a concentration system to produce a concentrated solids steam containing a mixture of magnesium hydroxide, residual minor amount of gypsum and regenerated crystalline inert material; 
 returning a portion of the concentrated solids stream to the magnesium-enhanced calcium slurry sulfur dioxide removal process while passing a remaining portion thereof to the oxidizer; and returning a further remaining portion of the concentrated slurry stream to a flue gas stream at a solids collection device selected from an electrostatic precipitator and a baghouse to react with sulfur trioxide present in the flue gas stream upstream of the wet scrubber.